Build question

I have a Polish kit I would like built, preferably into a shorty 16". Is there any reliability issues with the 16" builds? Do you re-thread the barrels or are you permanently attaching the flash hider to make length? If it could be threaded 5/8x24 it would be even better. How much to have one built? I wouldn't need it parked or painted I would do that. How do I get mine in line for the next build?